Credit: The Associated Press

This aerial photo taken April 28, 2011 shows tornado damage in Pleasant Grove, Ala. The photos and mementoes that were blown for hundreds of miles during the tornado outbreak two years ago are giving researchers new insight on how debris is carried.

ATLANTA — Photos and mementoes that were snatched up and blown hundreds of miles by a cluster of Southern tornadoes are giving researchers new insight on how debris is carried by the storms and how it could threaten the public.

A new study has documented one picture's flight of almost 220 miles over Alabama and Tennessee in 2011. That is among the longest-documented trajectories of tornado debris, the researchers found.